In Situ Forming of a 2D Inorganic Perovskite Capping Layer by Surface Reconstruction for Efficient and Stable CsPbI₂Br Perovskite Solar Cells

Although inorganic perovskite solar cells (PSCs) have made remarkable progress, ambient instability and serious nonradiative recombination loss greatly impede their further development. Herein, we develop a novel surface reconstruction process to in situ grow a 2D inorganic perovskite capping layer on a 3D CsPbI2Br perovskite surface via the dynamic methanol treatment and subsequent thermal annealing for simultaneously enhancing the stability and suppressing nonradiative recombination of inorganic CsPbI2Br PSCs. The dynamic methanol treatment removes the surface defective regions of CsPbI2Br perovskite and results in forming excessive PbI2 on the CsPbI2Br perovskite surface, and the subsequent thermal annealing triggers the surface reconstruction reaction of excessive PbI2 with CsPbI2Br that leads to in situ forming of a 2D CsPb2I4Br layer on the CsPbI2Br perovskite surface, which effectively decreases the defect density and enhances the stability of CsPbI2Br perovskite. As a result, the fabricated carbon-based CsPbI2Br PSC displays a power conversion efficiency of 14.29%. Moreover, the CsPbI2Br device with a 2D CsPb2I4Br layer displays superior stability, and the efficiency of the cell without encapsulation remains at over 90% of the original value after storing in ambient conditions for 900 h.